MOSCOW (AP) — A Russian lawyer who has defended a Ukrainian imprisoned for spying says a widely anticipated exchange of prisoners between Russia and Ukraine is underway.

A prisoner exchange could be a significant step toward easing Russia-Ukraine relations and raising chances for resolving the conflict in Ukraine's east where fighting between troops and Russia-backed separatists has killed more than 13,000 people since 2014.

Buses from a Moscow prison believed to be carrying Ukrainian prisoners arrived at the capital's Vnukovo airport on Saturday.

Attorney Mark Feigin tweeted that the exchange is underway and that the prisoners from the Russian side include 24 Ukrainian sailors who were seized by Russia in November, along with Ukrainian journalist Roman Sushchenko who he has represented and filmmaker Oleg Sentsov, convicted of plotting terrorist acts.